Film drum drive for photophonographic apparatus



Oct. 2,1945 E."IW.'KELLOGVG, 8

' FILM DRUM DRIVE FOR PH OTOPHONOGRAPHIC' APPARATUS Filed Dec. 17, 1945 2 Shets-Sheet 1 j Mike/209;

Gttomcg Patented Oct. 2, 1945 ries FILM DRUM DRIVE son" Pno'roriroNo- GRAPHIC APPARATUS Edward W. Kellogg, Indianapolis, Ind., asslgnor to Radio Corporation of America, a corporation of Delaware Application December 17, 1943, Serial No. 514,624

12 Claims.

This invention relates to a mechanism for driving the film drum of a photophonographic device, such as a film sound recorder or sound head, at a uniform speed so that sound may be recorded on or reproduced from the film with fidelity as to pitch.

The driving of such a film at a satisfactorily constant speed presents a special, and so far as I am aware,'a unique problem, for the reason that the feed of the film is ordinarily controlled by sprockets in order that several driving systems may operate instrict synchrcnism. For example the sound and picture are recorded on machines driven by separate synchronous motors, and in a single machine having intermittent movement at the picture gate, the film must body goes'up too.. When it is desired to take out irregularities in the motion of some element such as a record, carrying recorded sound, the

such as springs. If this is done, irregularities can occur in the speed of the driving system without point at which sound is recorded or. reproduced,

be driven at several points, and free loops of film 1 maintained between these driving points. This is possible in a simple and practical way, only by propelling the film by means of sprockets, driven through gearing. I

Sound recording is ordinarily done on fresh, unshrunk or substantially unshrunk film, while the sound is often reproduced from prints suffering from considerable shrinkage. This is particularly true in the case of sound motion pictures where the film has been repeatedly passed in front of'an intense light source. If the film is propelled and controlled by sprockets, which -themselves run at fixed speed, the number of sprocket holes fed per second must remain constant while the linear speed of the film varies in accordance with its length, or dependent on shrinkage. It is undesirable to reproduce or record the sound fromor on the film upon a spocket for the reason that the sprocket teeth themselves produce irregularities in the film motion. Therefore it has become almost universal practice to employ what are frequently called mechanical filters. The term filter is better known as applied to electrical circuits which have the property of permitting certain components of the current to pass while preventing the transmisappearing in the motion of the record.

A constant-speed driving system can be provided for film by carrying the film past the on the surfaceof a smooth drum on the shaft of which is, mounted a flywheel. It would be possible to drive the flywheel through gearing from a motor, with a spring interposed to act as the elastic element of the filter, but this would fix the speed of the drum at a certain R. P. M. and hence at a certain peripheral speed relative to the rotation rate of the sprockets. As has been explained, the rate of rotation of the smooth drum cannot be set at a fixed value, owing to variations in the actual length of the film for a given number of sprocket'holes. Therefore a system must be devised which permits the drum, at least over a limited range, to choose its, own speed in a manner depending on the amount of slack film in loops between the sprockets and the drum.

Experience has shown that systems wherein the rotation of a flywheel is controlled by fllm loops, are subject to oscillations, and it becomes necessary to introduce damping. In accordance with my present invention I couple the drum to the flywheel through a frictional coupling of a type which has inherent damping properties, and at the same time I operate the flywheel at higher speed' than the drum, and thereby make it possion of other components. The commonest form of filter is known as a low-pass" filter, which passes direct current freely while substantially eliminating all alternating currents above a certain frequency. The net eflfect is that rapid irregularities in the current are eliminated. The analogous mechanical system is an arrangement permitting continuous motion in one direction 1 but tending to take out jerks and irregularities. The springs of an automobile in cooperation with the mass of the bodytake up the shocks of the poad, but when the wheels go up along hill the One object of the invention sible to obtain the necessary inertia eflect with a lighter and smaller flywheel than would otherwise be required.

is toprovide a lightweightfilmdrum drive. 7 1 Another object of the inventionis to provide a film drive which will feed the film past the.

translation point at a uniform linear speed limited by the sprocket hole speed.

*Another object of the invention is toprovide afilm drive which is sufllciently light in weight to be incorporated in 16 mm. single system recorders, single film system 35 mm. recorders.

and other devices where minimum are important. M

Another object of the invention is to provide a film drive which is eflectively damped.

size and weight analogous in its action of thisinvention.

.Another object of'the invention is to provide a film driveincluding afiywheel on the film drum, the rotation of which is effectively damped.

Another object of the invention is to provide a film drum drive in whichthe torque has a dellniterelation tothe film speed.

Another object of the invention is to provide a, film drum drive which will be low in cost.

Another object of the invention is to provide afilm drum drive which can be quickly brought up tofull speed.

other and incidental objects" of the invention will be apparent from a reading of the following in the case of a damped driving system.

Figure 3 shows in front elevation the relation of the several elements in one embodiment of my invention. I

Figure 4 is a diagram of an electrical circuit to the mechanical system Figure 5 is a front elevation of a form of vth lnventionin which power is supplied to the drum by a motor, whosearmature furnishes the nec-' Figure 6 is .a side elevation of the form of th invention as showninFig. 5, and

Figure '7 is a modification of the invention, similar to Fig. 6 but having an additional flywheel directlyon the drum shaft.

Fig, 1 shows the relations in a combined motion picture projector andsound reproducing device, wherein continuously rotating sprockets are shown at I, 2., and! while an intermittent sprocket is shown at 4, which moves thefilm quickly from one picture frame to the next, allowing it sprocket 4' requires that there be plenty of slack sprockets geared together can it be assured that there will be a constant amount of slack film in these loops and in the loops 8 and I. .The sound drum is shownat It with a pressureroller at H which prevents the fllm'from slipping on the drum, while an optical system I! concentrates light on the film at the point ii. A photocell. notshown, receives the light which is transmitted through the film at point II and the out-- put ofth'e photocellis amplified to provide the audio frequency currents for operatingloudspeakers. It is the sound drum II which con trols the speed of the film as it passes'the reproducing point it, and systems for providing 7 constant speed are concerned with obtainingthe depending-on the shrinkage of the film. Asso- '45 film. in loops 6 and I. and only by employing oneness the velocity of the film as it passes through the reproducing point 13. The irregularities to which I have reference are those inherent insprocket tooth action plus imperfections in the pitch of the teeth and the perforations, eccentr'icities in sprockets, and imperfections in gears; 'Motion picture film is not perfectly'limp like a piece of thin cloth but has considerable stiffness and can act as a spring. -Hencethe' loops 8 and 9, especially if the roller arrangements-are designed with a view totaking full advantage of the inherent elasticity of the fllm, are effective as springs. If the drum l0 runs too slowly loop '9 is pulled tighter, and speeds up the drum, while if the drum runs too fast loop 9 acquires extra slack and'pulls forward with less than normal or average tension, or. in an extreme case loop I may become tight enough to pull back appreciably. It is obvious that considerable speed fluctuations at sprockets 2 and 3 can occur with no appreciable efiect on the drum speed but only slight pulsations in the'amount of slack in the loops I and I. As explained in my U. S. Patent Re. 19,270, power may be supplied to the shaft of drum ID in suitable magnitude for overcoming bearing friction but in such a manner that it does not fix the speed of the drum, or altematively the drum'shaft may be mounted in lowfriction' bearings so that the entire. power for running the drum can be supplied by tension in loop I without pulling this tight enough to cause it to becomeobjectionably stifl.

The system as illustrated-in Fig, 1, comprising the elastic properties of loops and the inertia efa frequency determined by the stifinessof the I loop and the mass; of the flywheel. The only known cure for this condition is to provide damping. One method of providing damping is to defleet the drum-pulling loop 0 by a flexibly mounta ed idler roller which will move when the tension on the film changes and to connect the movable roller to a dashpot or other energy-absorbing device. Thisconstruction is shown, inmy U. S.

Patent Re. 19,270, which also discusses the requirements for maintaining flexible loops.

Another means of producing damping is to associate with the drum shaft and flywheel, 1

cupy. In other words, damping requires forces which are in phase-quadrature with the purely elastic forces. Methods of providing damping efciated with drum II is a lywheel or rotary m bilizer indicated by the circle is.

For the immediate discussion we shall assume that ll represents a flywheel rigidly'attached to the shaft of druni II.- The system comprising the inertia efi'ect of flywheel M and elasticity of filmloops 8 and 0 constitutes a mechanical of the rotary stabilizer will presently be explained.

' stabilizer, is covered in the Hanna and Reynolds fective at the drum shaft are described in my aforementioned U.,S. Patent 19,270 and inmy U. 8. Patent No. 1,969,755, in C. R. Hanna Patent No. 2,003,048, in Reynolds Patent No. 2,013,100, and in Loomis and Reynolds Patent No. 2,019,117. It is desirable for a better understanding of the present invention to describe'brlefiy at this point the two most important formsof'flywheel dampers covered in the above-mentioned patents; The one, generally known as the Magnetic drive, is covered in U. S. Re. 19,270and 1,899,571; and the other, known as the Rotary K v The magnetic drive consists fundamentally in filter capable of out in 7 providing the dn m flywheel with a copper flange fect of the flywheel, 'is subject to oscillations at time being a graphical utilize a certain principle in common.

} broad sense.

spanned by the poles of a magnet which can be rotated around the same axis, but the magnetv is on independent bearings. Whenever there is relative motion eddy currents are produced in the copper flange which produce a dragging offeet proportional to the speed diilerence. The magnet is geared to the main driving motor, and

' stabilizer must resist rapid changes of speed, or in its speed is therefore not influenced by any possible reaction between it and the flywheel. Thus the'electromagnetic drag which clamps any oscillation of the drum flywheel reacts against the practicall "solid" magnet.

The magnets may be driven at'normal drum speed, in which case they will provide damping only, and the film will have to provide enough torque to overcome drum bearing friction. or

the magnet may be run somewhat above normal whileloop 9 would be relatively slack. Under these conditions the appropriate place for the pressure roller would be on the lowerside of the drum, as shown dotted at but a guide roller would still be needed at H. l

The magnetic drive applies a torque to the drum shaft which becomes less as the speed of the drum increases, or in other words it has a drool) ing characteristic as illustrated in Fig. 2. Such a driving system permits the drum to run at whatever speed is required in view of the film shrinkage, without too much change in the tensiorrin the loops, and at the same time provides necessary damping, the slope of the characterisrepresentation of the clamping resistance. 5

In the case of the rotary stabilizer a heavy flywheel is mounted on ball bearings inside a sealed'shell, the free space being filled with oil,

and the shell is locked to the drum shaft. The

damping force is exerted the free flywheel.

The magnetic drive and the between the shell and rotary stabiliger In both cases damping'is provided by coupling the drum shaft to a second coaxial rotating member through a coupling having continuously and aperiodically yielding characteristics, or what I shall for brevity, designate as a "viscous" pling, the word viscous being understood in a very The member to which the drum shaft is coupled is capable of rotating independently of the drum shaft, and is restrained, either by its own inertia or by positive comiectionto a driving motor, from participating in such snfall fiuctations in speed shaft rotation.

My present invention constitutes a new method of providing damping at the drumfsha'ft. It is described, in that the like the methods already drum shaft is coupled to ment, through a coupling properties, but differs another rotating olewhich has damping from the former systems in that the other rotating element is not coaxiaL.

and in that the coupling does not utilize viscous fluid, nor magnetic action. According to my invention I mount on the drum shaft a rubber tired wheel of suitable design, and maintain in contact with the rubber tire a wheeler roller, preferably of smaller diameter, whichfin turn'may be conasmay occur in the drum nected to a flywheel or may be driven, directly or indirectly, b an electric motor. In any case the contacting roller; must be capable of resistin: changes of speed,iust as the independent coaxial member of the magnetic drive or rotary other words have a high mechanical. impedance with respect to speed variations, just as an elec trical inductance offershigh impedance to cur: rent variations.

The damping properties of the connection through the rubber tire between the wheel and the roller'are due to a peculiar physical char-= acteria'tic of the rubber tire which renders its behavior very similar to that of the magnetic of" viscous drives above referred to. This characteristic came to my attention in the course of ex periments in which'a driving system with a rubber tire was being employedto rotate a disc rec 0rd, in which case it was desired that the speed i be constant or independent of load, but it was found that with increasing load the turntable ran more slowly although the small contacting roller ran at fixed speed. Especially important for the present application are the facts that the decrease in speed was found to be a continuous and linear function of the load torque, and that at moderatelylarge loads. the speed of the turntable althrough reduced, was as uniform as at no load,

provided the load itself wassteady. Such a relationship cannot be accounted for on the theory that:there is any slipping between the surfaces.

The efiect is apparently due to the elasticity of form ofthe rubber which causes it to yield tangentially at the point oi'contact with the driving pulley when a tangential force is applied. The effect of this deformation of the rubber tire is to cause a momentary and local change of surface speed oft-he rubber, relative to the average speed of the circumference. Suppose for example that power is being supplied from the small solid pulley to the larger rubber tired, wheel; just as a given part of the surface of the rubber tire reaches the pointer contact, it finds itself jerked forward by the action of the driving roller. After passing the polntcf contact, the elastic properties of theruhber cause it to be restored .to its normal shape. and during this period the point on the surface movesrelatively backward, or its forward motion is at less than average velocity. The

two deviations from normal velocity must of course have equal and opposite net effects on totalthe relative circumferences of. the two pulleys or travel, but the fact that the excess velocity occurs at the driving point, results in a lowered speed of the drive'n'pulley relative to the driving pulley, as compared with the speed as calculated from wheels; ,If no tangential force is being transmitted from one wheelto the other, there will be no tendency for the rubber of the tire either to be pulled forward or-held back at the contact point, and thus little if any departure from its normal speed. The deformations of the tire are, within a limited .range, directly proportional to the forces which produce them, and this relationship produces the result that the departures of speed ratio from the normal ratio are directly proportlonalto the transmitted torque, and this is true for both positive and negative values.

The action I have just described might be called slip, but if this term isused, it must be understood as'llke the,.; slip of an induction motor,

' which is a continuous i'unction of load, and is not like ordinary'slipping of contacting surfaces,

which is a discontinuous function of tangential m... with no definite relationship etween the force and the resultant velocity of slipping. If slipping of the ordinary kind took place it would defeat the purpose of the invention of producing uniform velocity, for any actual sliding would act irregularly.

In one respect the action of' the rubber'tire v drive is different from that of a viscous or magnetic connection. In the case of the last-mentioned couplings the speed difference bears a fixed relation to the transmitted torque independent of the absolute speed with which both members run. In other words, if the magnet runs R. P. M. and the flange is stationary, the torque will be the same as is exerted when the magnet runs 190 R. P. M. and the flange 180 R. P. M.

in me. 3, wherein various structural elements are omitted in order to-show the rollers. Film from a slack loop 0 is fed onto the drum it under a combination guide and pressure-roller II. The

" drum is drivenentirely by tension on the film loop 9 which is pulled by the sprocket 3 which runs at substantially uniform speed, being geared to the driving motor. 'The rubber tired wheel is indicated at ll. Resting lightly-against the rubber tire is a smaller roller ll on the shaft of I which is a small flywheel ii. The shaft of the flywheelruns in two low-friction bearings II in In the case of the rubber tirev drive the speed] diilerence is roughly proportional to the trans mitted torque multiplied by the average speed.

At standstill there is no creep orslip. If four inch-ounces results in 5 R. P. M. slip of the rub-1,

ber tired wheel when itis running at 90 R. P. M.,

the same torque would produce approximately 10' R. P. M. slip when the wheel is running 180 R. P. M. This diilerence between the previous viscous connections and the rubber tire drive is not of importance in the present application, since the drum always runs at substantially the same speed. I am here simply pointing out that the two damping systems are not necessarily alike in all respects. I The creep efl'ect just described bears some resemblance'to a property of rubber tires described and utilized by C. A. Hoxiein U. 8'. Patent No.

1,756,884 but is not the same nor does, it give the same result, nor is it,in my invention, used in the same way.

Apartfrom the essential feature of'introducev ing a viscous, coupling between the drum'shaft' .and another rotating pulley, and thereby providing damping of the otherwise oscillatory drum drive system, the rubber tire coupling system affords certain practical design advantages. For Y many applications it is desirable to obtain the required flywheel eflect by means of a small flywheel running at higher speed than that of the drum. This results in a major reduction in weight and some reduction in space requirements, since" the of the flywheel (measured in terms of movement of inertia.) necessary to produce a giveniinertia effect, varies inversely as the square of its speed relative to that of the drum. There are no methods of coupling between two 'noncoax'il shafts which do not themselves introduce rregularities. For the stepping up thespeed ofth'e flywheel gears are not to be considered, and most belting arrangements produce serious,

disturbances. generally due to the Joint or spice. Moderately satisfactory couplings have been obtained with frictional connection between metal ,a yoke l8 pivoted to the frameof' the machine atli, thus fixing the radial pressure at substantially the weight of the small flywheel and the 4 associated parts. If tests indicate that the pressure should diflfer from this it can be increased by use of springs or the positionof the contact point-20 can be shifted around to the side, where 4. A disturbance is indicated by alternator 25 acting through resistance 21, while a battery 26 supplies a continuous current analogous to the forward rotation of the drum. Most of the alternating current produced by alternator I5 is by-passed through capacitor II, which is analogous to the flexibility of film loop 0. The continuous current passes through inductance It which corresponds to the flywheel ll whose in-,

lertia tends to keep its rate of rotation constant.

The slip orcreep effect of the rubber tire corresponds to the effect of resistor 30 in multiple with the inductance 28. An meter is shown at 3i indicating that this is the'place in the electri-h cal circuit where we would like to have minimum current fluctuation, just as it is desirable to have minimum speed variation 'at the surface of drum It. In Fig. 3 there is .no considerable mass analogous to inductance 82 of Fig. 4. Hence the electrical analogof Fig. 8 would omit in ductance 32 and show the circuit closed through the dotted line a.

Anyone familiar with, elec-" trical' circuits will recognize that vif resistance. 30 is made extremely high or infinite, which would correspond to shared speed ratio and nocreeping, oscillations canexist through the circuit cornprising element 28 and il. It will also be recognized that such oscillations can be effectively roilersfvery carefully constructed-and finished. The coupling through a rubber tire. provided the tire has been carefully trued up by a grinding operation, and the pulley which it engages runs 1' true, has been found to be one of the best of 'known arrangements from the constant speed standpoint for coupling two shafts together for the transmission of small amounts of power.

It is thus a second feature of my present inventi'on that! provide the necessary damping properties in combination with a satisfactory means for operating the flywheel or other unistopped by employing a suitable value or resistance at 30.

Another-formof the invention is shown Figs. 5 and 6. In this case the rubber tired wheel is coupled to a pulley on the shaft of a driving motor 35, whose armature has sufficient moment of inertia to provide the desired flywheel eflects.

The same motor drives the sprockets 2 and I through gears 38, 31 and the chain belt 38 with,

formly rotating pulley at higher. speed than the drum shaft. I

In its simplest form my invention is illustrated its associated sprockets-It, 40. Although Fig. 6 does not show the exact location of chain 88, it is to be understood that it does not engage nor in- ,ierfere with the shaft of drum l0. Fig.- 5 shows this Coupling the rubber tired-wheel u to the driving motor instead of to a separate flywheel does not necessarily result in any complication of accuses mechanism, since a driving motor is always re-- quired. The speed of theshaft of the motor itself is in general very free from fluctuations, and

it thus serves the purpose without ordinarily requiring any additional high speed flywheel. The advantage of thus positively driving wheel It is largely in the fact that it provides veryquick starting for the entire mechanism.

It is in general desirable to throw the principal slaclr definitely either into the feeding film loop 8 or the pulling film loop 9, leaving the other loop under some tension, in which case the loop under slight tension will do the controlling oi?- the drum speed. The position of the pressureroller is determined in view of which loop is under the greater tension. For this reason the nodcadi speed ratio between wheel M and coupled roller 55 would in. general be calculated to be such that in' the absence of him drum it will run either slightly slower or else slightly faster than its normal range of running speeds with film in place. Fig. 5 is drawn to represent conditions when the drum is over-driven. Film loop 8 is under some tension and controls the speed of the drum, and there is considerable slack in loop 8. The pressure-roller is shown at as.

Fig. '1 is like Fig. 6 except for the addition of a flywheel ti mounted directly on the drum shaft. Although flywheel li is larger than the armature of motor 35, the latter supplies the major part w v of the total effective moment of inertia owing to its higher speed; It has been found in tests that the speed constancy can in general be incproved by the employment of such a direct mounted flywheel. .It has little ellecton slower fluctuations in speed but it can do considerable in the way of taking out small rapid fluctuations, which may be introduced through the film loops, imperfections in drum hearings, in pressure-roller action, and imperfection in the rubber tire drive.

Referring again to Fig. 4, the action of this direct-coupled flywheel is analogous to introducing inductance 32 into the circuit. It is evident that the reactance ofcoil ill will not completely stop fluctuations tending'tc passthrough ammeter 3t, because 29 is lay-passed by resistance to. The introduction of a second inductance at of that 29. This would correspond to the condition that the moment of inertia of flywheel H multiplied by the square of its normal speed should not exceed approximately A of the moment of inertiaassdciated with pulley l5 multiplied by the square of its speed.

In the design of a system of this kind, the problem is usually to get enough creep orslip. There are a number of factors which will increase the slip for a given transmitted torque,-

for example:

The soft tire should have a high coefllcient of friction and be deformed appreciably tangentially by light load.

The rubber tired wheel should have relatively low peripheral speed and preferably a. rather small diameter.

The tire should be narrow and thick and should have a small area of contact.

The high-speed pulley or shaft should be of. small diameter, particularly in relation to the size or the tire. "It should be preferably of the same order of magnitude as the thickness of the tire measured radially, say, within a factor of two or three. I

The area of contact should be small between 1 the tire and the high-speed pulley.

Although it is diflicult to set any specific values on these. details, the design should employ these several factors to a degree that tension in one of the film loops which is less than that which can lift be transmitted by a free film loop while still wheel which is mounted on the drum. shaft. It

may alternatively be on the engaging pulley, or rubber tires may be provided ,on both pulleys. The general efiects will be the same. I prefer the form which I have illustrated, for the reason that it iseasier to make a metal pulley accurately most important are a high degree of flexibility,

freedom iron: tendency to become permanently deformed, and su'fliciently high coemcient of friction to make it readily possible to avoid any actual slipping. It is not necessary that the tire be of a material having high internal losses, such. as Viscoloid. It may be of high resilient matem rial such as pure gum rubber, and the damping 1. Photophonographic apparatus, comprising an drive means, a record film carrier and an aperiag cclically 'yieldabie friction drive coupling the drive means and the record carrier, said drive including a member having a resilient tire of sufiicient thickness in relation to its softness, width, and area of contact and the diameter of said carrier 59 to obtain a speed differential of substantially three percent of normal operating speed when the torque being transmitted is of a magnitude less than that required to pull the film to a substantially straight line.

so 2. Photophonographic apparatus comprisinga drive means, a record film carrier, a flywheel integral therewith and an aperiodically yieldable friction drive coupling the drivemeans and the record carrier, said drive including a. member havso ing a resilient contacting element of suflicient thickness in relation to its softness, width, and contact area, and the diameter of said carrier to obtain a transmitted tor'que not exceeding that to which the film loop might be subjected without as impairing its flexibility.

3. Photophonographic apparatus comprising a drive means, a record film carrier, pulley means rigidly connected to said record mm carrier, relatively small pulley means connected to the drivemeans, and an aperiodically yieldable friction member on the pulley means of the record carrier, 8mm: the pulley connected to the drive means,

comprising a material elastic in form, inelastic.

in volume and having a thickness, width, and

6 J a a v cent'difi'eren-tlal in speed between said-two pulley means when the torque is not less. than that which would impair fiex'ibility of said film.

'4. Photophonographic apparatus comprising a i drive means, a record film carriena flywheel in;

tegral therewith, pulley means'rigidiy connected to said record film carrier, relatively small pulley means connected to the drive means and an aperiodically yieldablei'riction member on the record carrier engaging the pulley connected to the drive means comprising a material elastic in form, inelastic in volume and having a softness, thickness, width, and contact area to provide a substantially three percent difierential in speed between said two pulley means when the torque being transmitted is of a magnitude less than that required to pull the film to a substantially straight line.

a 5. ghotophonographic apparatus comprising an r inertiamember. a record film carrier and a rubber tire drive alone coupling the inertiamember' and the record carrier, said rubber tire having a thickness in relation to thesoftness of the tire material, the carrier diameter, thearea of ZOIl-r tact, and the'width of the tire to permit a, speed diil'erence of substantially three percent of nor-- mal operating speed when the torque being transmittedis of a magnitude less than'sufiicient to pull the'film to a substantially straight line.

6'; Photophonographic apparatus comprising a an inertia member, a record film carrier in the form of a sprocket, a second record film'carrier in the form of a smooth roller, a flywheel 'integral with said roller and a rubber tire drive alone coupling the-inertia member and the record l carrier, said rubber tire being of sufiicient thick;

nesg in relation to the softness oi the'tire mate-' I rial, the roller diameter, the area .of contact, and the width of the tire to permit a speed difierence 3 of substantially three percent 01' normal operating speedwhen the torque being transmitted to said roller is of a magnitude less than sufilcient to pull the film to a substantially straight lin between said sprocket and said roller.v

7. Photophonographic apparatus comprising a a softness, thickness, width, and contact area sufficient to provide a speed differential of subs'tantially three percent between said second mentioned record film carrier and said drive means when thetransmitted torqueis insufilcient to pull the film to' a substantially straight line between said sprocket and said roller.

8.. Photophonographic apparatus comprising a I 'a' speed diiference between said two pulley means of substantially three percent when the transmitted torque does not exceed that to which the film loop between saidsprocket and said carrier might be subjected'without impairing its flexibility; i p l 9. Apparatus for providing uniform speed of an elongated flexible record, comprising 9, smooth, drum to whichsaid record adheres by friction,

driving means, sprockets connected to said driving means, one of said sprockets pulling said record around said drum, said means providing flexible loops of said record on both sides of said drum, a wheel mounted on the same shaft with said drum, ,a pulley contacting the periphery of said'wheel, the wheel or the pulley being provided with a tire of flexible material, and means asso-, ciated with said pulley for causing it to resist changes of speed, said tire being of -sufiicient thickness in relation to its softness; width, and

contact area, and the diameter of said drum to 40 permit a speed difference of substantially three percent betweensaid drum and said'wheel when the transmitted torque does not exceedthat to I impairing its flexibility.

drive means, a record film carrier in the form of I a sprocket driven by salddrive means, a second record film carrier in the form of a smooth roller,

.pulley means on said second mentioned record film carrier, relatively small pulley means-con nected to the drive-means and a tire on the pulley means on the record carrier engaging said second mentioned'pulley connected to the drive means comprising amaterial elastic in form and having -ley.

11. Apparatus as described in claim 9 wherein which the film loop might be subjected without 10.: Apparatus as described in a flywheel is mounted said pulley is driven by an electric motor.

12. Apparatusas described in claim 9,inclu(1l-- sa d ing a flywheel mounted, on the shaft with drum. I

claim,9 wherein on the shaft of saidpul- 

